Recent studies have demonstrated that the right dorsolateral prefrontal cortex and the right temporoparietal junction are causally involved in social norm compliance: its activation corresponds with the third-party norm enforcement behavior, known as third-party punishment. The current study aimed to address the inconsistencies in effects of brain stimulation methods on right dorsolateral prefrontal cortex and right temporoparietal junction to clarify its role on third-party punishment. Despite a decade of neuroimaging research, the interaction between the right temporoparietal junction and right dorsolateral prefrontal cortex in third-party punishment remained unclear.  Here, we tested the hypothesis that a third party’s decision to punish norm violations depends on the activity of the entire right dorsolateral prefrontal cortex-right temporoparietal junction network. We used transcranial direct current stimulation to independently or jointly modulate right temporoparietal junction and right dorsolateral prefrontal cortex activity during the third-party dictator game. We found a significant effect of anodal transcranial direct current stimulation of the right temporoparietal junction, which decreased the third-party punishment of moderately unfair splits. Joint stimulation of the right temporoparietal junction (by anodal transcranial direct current stimulation) and right dorsolateral prefrontal cortex (by cathodal transcranial direct current stimulation) produced a marginal effect on third-party punishment. Our results suggested that the right temporoparietal junction could modulate the perceived moral costs of third-party punishment.